The prior art has recognized the potential of peat moss material for use as an absorbent medium in structures for absorbing body exudate, such as sanitary napkins. The peat moss material has highly desirable fluid absorption properties, such as a remarkable absorption capacity and the ability of "drying" adjoining materials by continuing to pull or wick fluid away from them over a long time period such that virtually all fluid is collected in the peat moss core. These attributes allow the material to provide highly efficient absorbent components which can be made relatively thin for better fit, comfort and discretion, while being sufficiently absorbent to prevent overflow leakage and garment staining.
The following United States Patents document the use of peat moss material for manufacturing absorbent components for disposable absorbent products:
______________________________________ U.S. Pat. No. INVENTOR(s) DATE ISSUED ______________________________________ 4,170,515 Lalancette et al. October 9, 1979 4,215,692 Levesque August 5, 1980 4,226,237 Levesque October 7, 1980 4,305,393 Nguyen December 15, 1981 4,473,440 Ovans September 25, 1984 4,507,122 Levesque March 26, 1985 4,618,496 Brasseur October 21, 1986 4,676,871 Cadieux et al. June 30, 1987 4,992,324 Dube February 12, 1991 5,053,029 Yang October 1, 1991 ______________________________________
The subject matter of these patents is incorporated herein by references.
Peat moss is a plant which grows from the top while the bottom part of the plant dies and gradually decomposes into peat. The modified VON POST method of characterizing the degree of decomposition of peat moss strata is the art accepted field test, described in detail in the "Peat Bogs of the Inhabited part of Roberval, Lac St-Jean, Dubuc and Chicoutimi Countries", a publication of the Ministere des Richesses Naturelles du Quebec, Direction generale des Mines, authored by Antoine Simard, Quebec, 1974. The subject matter of this publication is incorporated herein by reference.
As it is well known, peat moss beds, commonly referred to as peat bogs, typically have a vertical cross-sectional stratification. The top most layer of the bog is comprised of leaves, branches and flowers of living flora, predominantly the living peat moss plant but also including other plants growing on the bog. The top most layer extends to a depth in the range from about 2.5 centimeters to about 18 centimeters.
Below the topmost layer is a first intermediate layer consisting of undecomposed dead peat moss including the roots of other living plants. The first intermediate layer is characterized by being fibrous, relatively light coloured, with the plant structure generally intact. Such a layer extends typically from a depth in the range from about 35 centimeters to about 1 meter below the surface.
Below the first intermediate layer is located a second intermediate layer of partially decomposed peat moss which can generally be distinguished from the first intermediate layer by a clear line of colour demarcation. The second intermediate layer is characterized by increasingly darkening colour and increasing plant structure degradation as the depth increases, to a point where the plant structure is no longer apparent and it shades from brown to black. The lower portion of the second intermediate layer is typically a portion of the peat bog utilized as fuel. This layer extends from a depth in the range from about 1 meter to about 2.5 meters from the surface.
Below the second intermediate layer is the bottom layer which is the last stage of decomposition of the peat moss plant. The bottom layer is commonly referred to as "black earth" and is characterized by having essentially no discernable plant structure and a black colour. This material is found at a depth in the range from about 2.5 meters to about 4 meters from the surface. In some instances, peat bogs do not comprise this layer.
The modified VON POST scale assigns values to each stratum of the peat bog, from H-1 to H-4 with increasing degree of decomposition. The test consists of pressing samples of each peat moss stratum and examining the expelled water. An H-1 value is assigned to the top most layer which releases a clear liquid. An H-2 value is assigned to the first intermediate layer which releases a dirty liquid but substantially free of large organic particles. An H-3 value is assigned to the second intermediate layer containing peat moss in an advanced stage of decomposition, which when compressed, expels a muddy water containing brown and black organic particles. Finally, an H-4 value is assigned to the bottom layer which when pressed in the hand freely flows through the fingers.
Peat moss material for use in manufacturing absorbent components for disposable absorbent products is harvested from the peat moss bed and baled into blocks which are transported to the processing site where the peat moss material is refined and converted into absorbent material in continuous sheet form, the so-called "board". In a board form, the peat moss absorbent can be directly processed in high speed automatic equipment to assemble the disposable absorbent products.
To reduce transportation costs and facilitate the handling of the peat moss bales, it is desirable to dewater the peat moss material immediately after the harvesting operation in order to reduce its weight. One possibility is to provide at the harvesting site a mechanical press for compacting the peat moss crop and forcibly expel water absorbed in its fibers. However, the industry has always questioned the feasibility and the practicality of this dewatering technique on the grounds that peat moss material is a natural absorbent having excellent fluid retention properties and it is difficult to dewater by mechanical means.